Cyanate ester resins are generally considered to be high performance thermosetting resins at least to the extent that they usually exhibit high glass transition temperatures. In some applications such as in electrical laminates and the like it is desirable that they exhibit high fire retardant properties in that it is desirable that they exhibit an Underwriters Laboratory test no. 94 rating of V-0. The current industry standard cyanate ester resin is based on bisphenol A.
A typical method for obtaining ignition resistance in cyanate ester systems has been by the addition of brominated epoxy resins as disclosed by R. Kubens et al. in U.S. Pat. No. 3,562,214. Unfortunately, the addition of epoxy resins can result in a lower glass transition temperature, a decreased onset of thermal degradation, and a loss in moisture resistance with a corresponding increase in dielectric constant for the blended system.
Blends of non-brominated cyanate esters with brominated cyanate esters are disclosed by C. Burkhards et al. in U.S. Pat. No. 4,097,455, by G. W. Bogan and G. A. Monnerat in U.S. Pat. No. 4,806,625 and by J. P. Godschalx et al. in U.S. Pat. No. 4,782,178: however, this method to achieve flame resistance can be expensive. Blends of cyanate ester resins with ethylenically unsaturated reactive brominated monomers are disclosed by G. W. Bogan and P. A. Lucus in U.S. Pat. No. 4,746,727: however, some of these monomers, like bromostyrene, may suffer from volatility problems. Moreover, these approaches may still experience similar losses of performance as enumerated above with the brominated epoxy blends, or they may suffer from a lack of availability.
It would be desirable to have available, a cyanate ester resin composition which (1) has excellent flame resistance without an unacceptable sacrifice in the physical, thermal, electrical and moisture resistance properties which renders these cyanate ester resins desirable in such applications, (2) at the same time be reasonably affordable in terms of cost, and (3) maintains handling characteristics of an unmodified cyanate ester resin.